Findings published in the NEJM indicate that Pfizer and BioNTech's widely used COVID-19 vaccine Comirnaty marginally increases the risk of heart inflammation, although the risk is higher among those who contract SARS-CoV-2 infection, as reported in Yahoo!News.

Data from Clalit Health Services, a large Israeli health maintenance organization, show that for every 100,000 individuals who get the vaccine, 1 to 5 will likely develop myocarditis who would not otherwise have developed it.

However, among people infected with the coronavirus, researchers said the rate is much higher, at 11 cases per 100,000.

The researchers compared adverse event rates in 884,828 vaccinated individuals and an equal number of unvaccinated people.

Overall, 21 people reported myocarditis in the vaccinated group - mostly young men - compared with six people among the unvaccinated.

Investigators also analyzed adverse event rates in more than 240,000 infected patients, with results there indicating that COVID-19 is itself a very strong risk factor for myocarditis, and it also substantially increases the risk of other serious adverse events.